1. Field of the Invention
The present invention relates generally to printing, and more particularly to a card cleaning device for use in a card printer.
2. Prior Art
A conventional image forming device, such as a printer, sometimes includes a cleaning mechanism for cleaning the printable media which can be plastic, polyvinyl chloride (PVC) cards or the like before text, graphics or bar codes are applied to the media. Printable media may have one or two printable sides depending on the application. Some printable media have greater tolerance to pollution, such as dust particles, on the printable surfaces of the printable media and are still receptive to the printer for printing images thereon even through the printable surfaces of the printable media might not be very clean. Printers may use a ribbon mechanism for transferring images to the paper surfaces or an injection mechanism for depositing carbon particles on the paper surface to form images. The carbon particles ordinarily are well defined during printing and do not disperse once deposited on the surface of the paper. Thus, a light deposition of dust particles does not degrade significantly the printed image on the paper surface.
Other types of printable media, such as PVC cards, are particularly susceptible to pollution, i.e. the printable surface(s) of the PVC card must be maintained clean before printing to achieve acceptable print quality. Normally, these printable media, e.g., the PVC cards, require a high temperature thermal printing process to form images. Ordinarily, the temperature of the thermal printing process used to form images on these plastic printable media is very high, often much higher than a temperature of the thermal printing process, if any, needed to print on regular paper. As a result, if the printable surfaces of these printable media, e.g., the plastic cards, are not clean, the images printed thereon tend to be blurred due to this high temperature process. Even a slight deposition of dust particles on the printable surface of the plastic card will likely blur the images to be formed and greatly affect the quality of the printing results. Thus, having a cleaning mechanism is necessary for the printer adapted to print PVC cards.
The cleaning mechanism in a conventional printer typically is located inside the printer and is adjacent to a feeding mechanism. The feeding mechanism of the printer is accessible from outside for loading or unloading a printable medium stack onto the feeding mechanism. During operation, the feeding mechanism feeds the printable media, such as cards, into the printer to be printed by a print head of the printer. The cleaning mechanism of the conventional printer is coupled to the conventional printer between the feeding mechanism and the print head. Therefore, the cleaning mechanism may clean the printable medium, such as a card, fed into the printer before the card is printed by the print head.
The conventional cleaning mechanism typically includes a cleaning roller and a drive roller rotatably coupled to a support frame securely mounted to the conventional printer. The cleaning roller and the drive roller are approximately positioned in parallel to each other. The drive roller normally is rotatably coupled to the support frame and cannot be moved either laterally or vertically. The cleaning roller, however, is often rotatably coupled to the support frame by coupling both ends of a cleaning roller shaft of the cleaning roller to the support frame. The cleaning roller is properly located so that it can be positioned directly above the drive roller and is adapted to press the printable medium against the drive roller. Moreover, positions of the drive roller and the cleaning roller inside the printer are precisely disposed to allow the printable media traveling there between. A drive roller shaft of the drive roller is coupled to a gear system of the conventional printer for rotation, and the gear system is further coupled to a motor of the printer, where the motor is adapted to control the rotation of the drive roller.
When the printable medium, such as a card, is fed into the printer by the feeding medium, the card will urge the movable cleaning roller slightly up by approximately the thickness of the card. Due to the compression effect, the cleaning roller will press the card against the drive roller located underneath. The cleaning roller is typically made by silicone materials molded to the roller shape for encircling the cleaning roller shaft. In addition, a treatment process is applied to the cleaning roller for making the silicone surface of the cleaning roller sticky. The above-mentioned treatment process is well known to persons skilled in the art and is not an aspect of the present invention. Most commercially available printers incorporating the cleaning devices have the drive rollers made of the same materials as are commonly used for making the platens of the printers. When the drive roller is rotated by the motor, it drives the card toward the print head. As mentioned, the cleaning roller presses the card against the drive roller, so when the card is driven through by the drive roller, the card will cause the cleaning roller to rotate due to the sticky effect of the silicone surface of the cleaning roller.
Moreover, the sticky surface of the cleaning roller serves the purpose of removing undesirable pollutants, such as dust particles, deposited on the printable surface of the card. When the card moves through between the cleaning roller and the drive roller, the cleaning roller would pick up dust particles deposited on the surface of the card facing the cleaning roller due to the sticky effect of the cleaning roller. Thus, the printable surface of the card should face the cleaning roller for cleaning. Alternatively, drive rollers of some conventional printers are made of sticky silicone materials similar to the cleaning roller. As a result, the drive roller and the cleaning roller of these printers are adapted to clean opposite surfaces of the card. The printable surface of the card may therefore face either up or down for cleaning, or both sides of the card could be printable surfaces.
The sticky surface of the cleaning roller removes dust particles from the card surface by sticking the dust particles out of the printable surface of the card as the card rolls through the cleaning roller. After being removed from the card, the dust particles will stick to the surface of the cleaning roller. As a result, the surface of the cleaning roller accumulates more dust particles each time the cleaning roller cleans a card, and the efficacy of the cleaning roller is accordingly reduced after each cleaning. At some point in time, the cleaning roller will no longer be able to effectively remove any more dust particles from the cards due to the dirtiness on its surface. The cleaning roller, therefore, needs to be clean, or even be replaced, periodically to maintain the effectiveness of the cleaning device of the conventional printer.
As stated, the cleaning roller is coupled to the printer by inserting its cleaning roller shaft into a pair of slots on the support frame of the printer. Generally, the slots are located deep inside the printer, so it is quite difficult and inconvenient to install, to replace, or to remove the cleaning roller for cleaning or for maintenance purposes. Since the drive roller is positioned underneath the cleaning roller in the printer, it is even harder to remove or to replace those drive rollers that also serve the function to clean the cards and therefore need to be cleaned periodically. Moreover, the size of the cleaning roller in a typical conventional printer is quite small. Usually, the cleaning roller has a width of approximately 2.4 inches—slightly wider than the width of a regular business card, and it has a diameter of approximately 0.6 inches. Thus, the cylindrical surface of the cleaning roller gets saturated by the dust particles quite easily because the surface of the cleaning roller is quite small, and the cleaning roller needs to be cleaned frequently. Thus, the need arises for a card cleaning device (or cartridge) that provides easy access for maintenance, occupies a relatively small space inside the printer and eliminates the need for frequent maintenance of the cleaning rollers.